Tetrapod Zoology

What with the recent articles here on tree-climbing dinosaurs and dromaeosaur tails it seems appropriate to post this image, taken in a German museum (but unfortunately I can’t remember which one: let me know if you do). I don’t know anything about the mount, but I guess that the people behind it wanted to present the idea that dromaeosaurs might have been in the habit of climbing on their prey during acts of predation, an idea since discussed more seriously by Manning et al. (2006) (although they proposed that the sickle-claws actually functioned as climbing crampons)…

i-f31c2f1113874a808821cf070c4b84cd-proof_that_dromaeosaurids_can_climb.jpg

Incidentally – I’m hardly the first person to say this – but I think the whole ‘dromaeosaurs were macro-predators’ thing (depicted here) is often overdone in the literature and in reconstructions. Giants like Utahraptor were, no doubt, in the habit of dispatching large prey, but the idea that Deinonychus made a living by killing adult Tenontosaurus and nothing else misses the point that large predators eat an awful lot of small and mid-sized prey.

Anyway, am busy busy busy here in the run-up to SVPCA, and mostly occupied in ‘research time’ by azhdarchids and their avian analogues. It will all be over all too soon.

Ref – -

Manning, P. L., Payne, D., Pennicot, J., Barrett, P. M. & Ennos, R. A. 2006. Dinosaur killer claws or climbing crampons. Biology Letters 2, 110-112.

Comments

#1 Mike Keesey
August 27, 2008

Since when are crampons laterally compressed?
#2 jck
August 27, 2008

Interesting case of convergent evolution. I’ve had cats who do the same thing. I wonder if juvenile dromaeosaurs did that when ornithopods were holding cans of wet food.
#3 Bob B.
August 27, 2008

Well, like I said in the previous thread, I think they may have climbed trees. Not sure about climbing prey. No matter how large, prey are usually moving and I doubt they would risk injury by jumping, latching on, and climbing a moving object.

Dogs may chase cars, but they very rarely catch one…

Perhaps in their tree-climbing endeavors, dromaeosaurs pushed the prey they were chasing to take up flight at some point in their evolution and then dromaeosaurs, too, developed the gift of flight in order to catch them.

Just some thoughts.
#4 Nathan Myers
August 27, 2008

Silly, they didn’t climb sauropods to eat them. They climbed to surf them. Even Fred Flintstone knew that.

Anyway, if you hope to eat one, just pop the balloons at the base of its neck so it can’t hold its head up any more. Mind the exploding cranium, though.
#5 Stevo Darkly
August 27, 2008

A few years ago there was some kind of “dinosaurs of Russia” (including Mongolia)exhibit that was touring the USA, so I got to see it. It included a mount of a Deinonychus in a similar position, but climbing the trunk of a tree.

Although I’d previously heard the hypothesis that dromaeosaurs might have been tree-climbers, that was the first time I ever actually saw it depicted. At the time I found it very unconvincing, but after getting used to it I see it as much more likely now. (The tree-climbing, not necessarily the megaprey-climbing.) It was the revelation of the close affinity between dromaeosaurs and volant birds that convinced me, I think.

I am also intrigued by the fact that the extinct carnivorous mammal Thylacoleo is the only other type of animal other than dromaeosaurs to to have sport such a prominent pair of sickle-shaped claws (as far as I know), and Thylacoleo is supposed to have been a good climber. Any parallelism going on there?

I wonder if dromaeosaurs generally tended to live a catlike lifestyle, sometimes taking to the trees for safety, storing food or perhaps active hunting.
#6 kad
August 27, 2008

Bob said: “Well, like I said in the previous thread, I think they may have climbed trees. Not sure about climbing prey. No matter how large, prey are usually moving and I doubt they would risk injury by jumping, latching on, and climbing a moving object.”

Bob, I’m not sure I buy the notion that dromaeosaurs made a living by climbing large prey either, but keep in mind all macropredators risk injury (and many are injured) when they hunt large prey. Afterall, “jumping, latching on, and climbing a moving object” is the way lions attack a cape buffalo for instance. The risk of injury is something macropredators have to live with.
#7 Jenny Islander
August 27, 2008

I wonder if their hunting strategy for big prey might have been “mob it, jump on, do some D, drop off, run out of range, wait for it to weaken, then eat it.” Dogs, not cats.
#8 JuliaM
August 28, 2008

“I wonder if their hunting strategy for big prey might have been “mob it, jump on, do some D, drop off, run out of range, wait for it to weaken, then eat it.” Dogs, not cats.”

Or large monitors…?
#9 Mark Lees
August 28, 2008

Dromaeosaurs riding sauropods! Using their sickle-claws as crampons?

Ok, do you recall the wormrider scenes from Dune? Where Paul Atreides (after he becomes Muad’Dib) gets to ride the Shai-Hulud (sandworm). I now have this picture of juvenile dromaeosaurs going through a coming of age ritual involving summoning and riding sauropods.

Personally I find the idea that they hunted large prey unconvincing. I still like the comparison with ground hornills – and see them feeding on small vertebrates and large invertebrates with a bit of opportunistic scavenging.
#10 Jerzy
August 28, 2008

It remembers me of neighbor’s dog doing this to his master. Another meaning of word “raptor”?

BTW, how good were these half-mobile forelimbs in grasping and climbing vertical objects?
#11 Ian Tindale
August 28, 2008

As someone who has been attacked and mugged by a group of what amounted to varying sized and aged youths, once there’s a certain amount of them, you just can’t defend with any useful strategy. If these hounded their prey by climbing, aren’t they’re likely to have done so in (sort of) organised packs whose numbers exceed a critical mass?
#12 chris y
August 28, 2008

These things roost and nest in trees, although they generally forage on the ground (not eating large herbivores unless they’re already dead), and they’re probably bigger and heavier than Velociraptor. There’s a lot to be said for being out of the way of lions and tyrannosaurs when you’re asleep or raising nestlings. So it seems perfectly reasonable to me that mid-sized maniraptors would have climbed, because they would have been a bit rubbish at flying.
#13 David Marjanovi?
August 28, 2008

and Thylacoleo is supposed to have been a good climber. Any parallelism going on there?

Would surprise me. The reason we think Thylacoleo was a good climber is its anatomy — for example the opposable thumb –, which does not fit dromaeosaur anatomy very much at all.

Since when are crampons laterally compressed?

Indeed. And since when do they point downwards? Remember, it’s not a monkey, it can’t put its feet any way it wants. The same holds for the hands: grasping a tree trunk or leg was easy, but like all theropods to this day, dromaeosaurs weren’t able to rotate their forearms and thus weren’t able to unlock a door.

Perhaps in their tree-climbing endeavors, dromaeosaurs pushed the prey they were chasing to take up flight at some point in their evolution and then dromaeosaurs, too, developed the gift of flight in order to catch them.

What would that prey be?

It was the revelation of the close affinity between dromaeosaurs and volant birds that convinced me, I think.

How much does climbing really have to do with flying…?
#14 David Marjanovi?
August 28, 2008

These things roost and nest in trees [...], and they’re probably bigger and heavier than Velociraptor.

Yes, but they don’t climb. They fly instead.
#15 chris y
August 28, 2008

Yes, they fly, but most dromaeosaurs couldn’t. That’s why, if the dromaeosaurs wanted to put thin air between themselves and their predators for safety’s sake, they would have had to climb. Like large, terrestrial primates, for another analogy.

The point I’m grasping for is that most of these things were relatively small animals which would have been extremely vulnerable on the ground if they were sleeping or had dependent young. All the hypotheses for their behaviour I’ve ever seen concentrate on their own predation strategies rather than predator evasion, which seems incomplete.

The point about the Marabou is that nobody bats an eyelid at the idea of Microraptor in a tree, because we see things the same size and general shape in trees all the time, but you have to look a bit harder to find potential arborial Velociraptor analogues these days. But there’s no certainty that Microraptor could have flown up into one, even if it could glide down. Climbing just seems to make a whole lot of behavioural sense.
#16 Jerzy
August 28, 2008

“but you have to look a bit harder to find potential arborial Velociraptor analogues these days.”

Dinosaurs were bipeds. Crampon claw can be attempt to link effective terrestial and scansorial locomotions in bipeds. In the same way, no species of bat or pterosaur combines running with flying in the way of birds.

Only parallel are tree kangaroos, but their feet were already too modified in terrestrial ancestors.

BTW, coming back to implausibility of hypothesis that claws of dromaeosaurids were hunting tools. Was Velociraptor able to see his feet when holding prey? Or arms got on the way and he had to kick blindly?
#17 johannes
August 28, 2008

> The point I’m grasping for is that most of these things
> were relatively small animals which would have been
> extremely vulnerable on the ground if they were sleeping
> or had dependent young.

In spite of the popular opinion that ‘raptors’ were invincible killing machines that came from planet Krypton, were smarter than humans and could open doors, there is fossil evidence that small maniraptorans suffered from predation, see here: http://earth.geology.yale.edu/~ajs/1993/11.1993.08Elzanowski.pdf, scroll down to page 238 and try to ignore the stuff about troodontids and spinosaurids being sister groups. Note that the culprit (for the killing of the little maniraptoran, not for theories on theropod relationships that were perfectly legitimate in 1993, but look positivly odd 15 years later) in this case was probably a deltatheroid, without doubt a competent predator, but hardly a monster.
#18 B
August 28, 2008

kad: Yes, I realize that, but these were a lot smaller compared to their prey. If they used their sickle claw as a weapon, I always imagined them having more of a “slash and run” approach. Maybe a small pack were following a sick or young animal and they would take turns running at the prey and giving it quick slashes then running off a bit. Done in the right spots on the body, they would probably bleed to death before the predators exerted too much energy.

The images of a swarming approach, like flies, on the back of a tenontosaur always looked a little too “Hollywood” to me.
#19 johannes
August 28, 2008

Should the link to the pdf don’t work, try again here:

http://earth.geology.yale.edu/~ajs/1993/11.1993.08Elzanowski.pdf
#20 Darren Naish
August 28, 2008

I think that dromaeosaurids and others maniraptorans were probably capable of occasional, opportunistic tree-climbing, mostly because I can’t see any good reason why they weren’t. They had sharp claws on hands and feet, flexible fingers and toes, a reasonable degree of rotation and abduction in the forelimb, and a good sense of balance, and even animals of Deinonychus size (total length 3 m, weight maybe 40-70 kg) aren’t too big to get into large trees. The absence of a pronatory ability in the forelimb isn’t a problem given that there are extant climbers that climb with their palms directed medially (including cats and mustelids).

However, I don’t think that the sickle-claws were anything special to do with climbing. I’m still unhappy with the recent proposal that the sickle-claws functioned as specialised climbing crampons: hats off to the team involved for using some science to test claw function, but I disagree with the assumptions they made about the morphology of the keratin sheath, and with their assumption about the way in which a dromaeosaur may have deployed its sickle-claw in predation, and with what they said about claw morphology and function in extant predators. For more see the old comment here. Climbing up onto giant prey seems like one of the dumbest things ever, plus it assumes that dromaeosaurs are dedicated killers of big prey and not much else. What are the dromaeosaurids meant to do once they climb up onto the side of a tenontosaur? Start gnawing away at the tough bony ridge along the animal’s back?

Anyway… last time this subject came up in the comments it turned into a protracted argument with Paul Barrett. We still disagree on this subject.

Johannes noted a maniraptoran specimen that may have been killed by a mammal. The specimen concerned is Archaeornithoides: note for the record that most recent workers have regarded it as a juvenile troodontid, not as a dromaeosaurid… but the point remains, and I’m not disagreeing with Johannes’ point about the lack of super-powers in maniraptorans.
#21 Nick Gardner
August 28, 2008

chris y

You are making higher-level inferences without data to back it up.

To re-emphasize for your consideration from David Marjanovi? ‘s comments earlier:
“Remember, it’s not a monkey, it can’t put its feet any way it wants. The same holds for the hands: grasping a tree trunk or leg was easy, but like all theropods to this day, dromaeosaurs weren’t able to rotate their forearms and thus weren’t able to unlock a door.”
#22 Zach Miller
August 28, 2008

The big question I have about the sickle-claws is this: What the heck was their original use? They’re apparently present in the Paravian ancestor (or at the very least, the Deinonychosaurian ancestor). Were they used for killing prey? If that’s the case, then why didn’t other theropods groups evolve retractable sickle claws?

Now, the first paravians, exemplified nicely by Mahakala (love that name–it’s fun to say), were tiny little magpie-sized theropods. But they still had sickle claws! As did Archaeopteryx, but to a lesser extent. The urvogal, from what I can tell, had the “retractable” part, but lacked the big ol’ sickle claw. So what good is a retractable toe?

Maybe the retractable toe in some way makes tree-climbing a little easier. This would assume that arboreality is also basal to the paravians. Anyway, maybe a sickle-claw can dig into bark better than a normal-sized claw (no reason it wouldn’t). I’d bet my bottom dollar that sickle-claws were tree-climbing aids before the advent of flight, when tree-climbing was a necessity.

Why? There’s a correlation between potentially arboreal theropods (paravians) and a sickle-claw. And it’s not enough to say that the sickle-claw was for killing stuff, because tiny little paravians had a sickle claw. Mahakala wasn’t attacking Psittacosaurus! And besides, like I said before, why didn’t other theropod groups evolve a sickle claw if sickle claws were so advantageous in killing prey?

No, I think the sickle-claw must have initially appeared for a purpose apart from killing prey. Tree-climbing seems like a good fit. And like Darren said, there’s no reason to think that larger dromaeosaurs weren’t also climbing trees. they could have used their sickles in the same manner. Bigger theropod, heavier load, bigger sickle claws…?
#23 David Marjanovi?
August 28, 2008

I should have mentioned that everything I said also holds for Microraptor. Sure, M. was so small that it should have automatically had a fairly easy time climbing, and the proportions of its toe bones are not like those of dedicated runners — but they aren’t like those of dedicated climbers either, and other adaptations to climbing are lacking. IMHO it did more flying than climbing.

Anyway, maybe a sickle-claw can dig into bark better than a normal-sized claw (no reason it wouldn’t).

Not just into bark, but through the branch on which the animal is standing!

Imagine tying a sickle to each of your feet in a vertical position and then climbing a tree so that your weight is supported by the cutting edges of the sickles. I still don’t get why anyone ever considered this a good idea.
#24 Zach Miller
August 28, 2008

Okay, well, look at it this way. A dog’s claws point roughly straight out. They do not curve downwards (toward the ground). A cat’s claws DO. Theropod toe claws are generally more like that of a dog’s. However, paravians have a “sickle-claw” that angles downward like a cat’s. Cats climb trees by using their claws to “dig in” to the bark of the tree. At no time do they end up accidentally chopping a branch off.

I have a cat with its hind claws intact. When you look at a cat’s claw, the underside more or less comes to a point, so that the claw would be teardrop-shaped in cross-section. I imagine it’s the same situation with dromaeosaur sickle-claws. Only the point of the claw would penetrate the bark. The paravian wouldn’t be hanging from its sickles (I really need to draw a picture–maybe I’ll blog about this later). Rather, the entire foot, metatarsals and all, would be flat against the side of the tree. While the claws of digits III and IV didn’t really have much of an effect on the bark, digit II’s claw curves downwards and pierces the bark like a cat’s claw.

A cat’s paw is also flat against the tree. Without its claws, it wouldn’t be a very good climber!

Again, I really need to draw some pictures…
#25 Karl Zimmerman
August 28, 2008

As a total aside, has any work been done hypothesizing that the retroverted pubis of Paravians was a climbing adaptation?

It just struck me that the conventional theropod pubis would be really bad for climbing a tree trunk vertically, as would mean the “boot” of the pubis would be the lowest point on the torso. Imagine if you were trying to climb a tree trunk with a foot-long codpeice sticking straight out from your crotch. Essentially either the theropod would have to hold its upper body far from the tree trunk, or tilt its upper body in towards the trunk in a very unnatural manner.

In contrast, the retroverted pubis of paravians means the lower belly is much shallower. Because of this, the belly is essentially flat. When climbing up a tree trunk (or whatever) both the upper and the lower body could be equally close to the trunk.

Provided the ancestral paravaian needed to climb trees to escape predators, I could see this difference being enough to select for an increasingly-retroverted pubis.
#26 William Miller
August 29, 2008

Yeah, super-powered raptors always bothered me, even though [i]Deinonychus[/i] is my favorite dinosaur. (Especially in Jurassic Park 3 – they’re even more so there than in the first two.)

I remember trying to convince someone that [i]Tyrannosaurus[/i] could not, in fact, defeat a tank.
#27 Andreas Johansson
August 29, 2008

If the sickle claw is for climbing, why only have one per foot? There would seem to be an obvious advantage in having multiple anchoring points when climbing.
#28 David Marjanovi?
August 29, 2008

If it’s for climbing, why can the 2nd toe be hyperextended and hyperflexed so far?
#29 TheBrummell
August 29, 2008

Day 13:
We have successfully established base camp. My porters seem quite excited about the prospects for tomorrow’s climb. My colleagues, on the other claw, seem more concerned about the “big push” planned from Camp 3, once we’ve established that much progress.

Day 15:
Camp 2 tonight, sadly not as far up the climb as we had hoped. Most of the delay is the fault of my increasingly-useless personal servant, who was nearly crushed this morning by a forefoot.

Day 16:
Big push tomorrow, on to the head. All of us in the camp are quite excited, and I had to convince Manuel to stop sharpening his pitons as they were shrinking at an alarming rate under his care.

Day 18:
Disaster! This climb must be aborted, due to all the death and failure we have encountered over the last three days. My family will be sorely disappointed by my failure to bring home the promised many tonnes of fresh meat.
#30 Jaime A. Headden
August 29, 2008

I am surprised this theory of dromies riding sauropods hasn’t been proposed before. Imagine them acting like Freemen riding Great Makers, only they don’t need to use grappling lines (since they have it built in). Now all they need is a Mesozoic thumper.
#31 Derksen
August 29, 2008

I’m curious: given that folks are interested in maniraptors as vertical climbers and leapers, has any sort of comparison been done to extant VCL prosimians like lemurs who might occupy a similar ecological niche? I’d suspect that the maniraptors’ carriage suggests more of an intermediate lifestyle that spends more time on the horizontal, but I’ve (unfortunately) been out of primatology for years. Might there be an appropriate prosimian model?

If not, would anyone like to dismiss this amateur theory out of hand, and explain the morphological differences between the two groups adaptations in both phalanges and the shoulder/pelvic sockets for limbs?
#32 Jerzy
August 29, 2008

Yes! We knew that sauropod herds migrated long distances. Now we learned that little maniraptorians travelled by hitchhiking on sauropods back, migrating with seasons.

I imagine sauropods walking through Mesosoic landscape with string of maniraptorians riding along their back. From little ones on nape to Deinonychus on rump.

Or two species of maniraptorians (say, troodons and microraptors) fighting who kills the same sauropod? Pushing and kicking each other while hanging on sauropod sides, like Indiana Jones movies?

Gosh, that is frivolus nonsense.
#33 David Marjanovi?
August 30, 2008

Lemurs have ordinary mammalian hip joints, which means they can move their legs in lots of directions. Dinosaurs generally are almost incapable of any degree of sprawling. The mobility at shoulder joint of dromaeosaurs was similar to that of modern birds, except that the arms AFAIK couldn’t be lifted much above horizontal.
#34 Jerzy
August 30, 2008

Birds compensate it by extreme motility at “ankle” and “foot” joints or tarsometatarsal and digital or whatever these two are called.

Watch how songbird (say, reed warbler, or simple starling or sparrow) moves its joints when perching on branch or reed. Improbable.

How these were in maniraptorians?
#35 martian
February 28, 2009

Nicely found Mark Lees.
#36 Nick Gardner
August 31, 2009

“I wonder if their hunting strategy for big prey might have been “mob it, jump on, do some D, drop off, run out of range, wait for it to weaken, then eat it.” Dogs, not cats.”

Or large monitors…?

Except apparently big monitors don’t do this either. See Fry et al. (2009) for a discussion of this myth in komodo dragons.

http://dx.doi.org/10.1073/pnas.0810883106
#37 Marco Tedesco
September 4, 2010

The museum is the Braunshweigishes LandesMuseum of Braunshweig,Lower Saxony,right?